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#ifndef KOKKOS_IMPL_SINGLETASKQUEUE_HPP
#define KOKKOS_IMPL_SINGLETASKQUEUE_HPP

#include <Kokkos_Macros.hpp>
#if defined( KOKKOS_ENABLE_TASKDAG )


#include <Kokkos_TaskScheduler_fwd.hpp>
#include <Kokkos_Core_fwd.hpp>

#include <Kokkos_MemoryPool.hpp>

#include <impl/Kokkos_TaskBase.hpp>
#include <impl/Kokkos_TaskResult.hpp>

#include <impl/Kokkos_TaskQueueMemoryManager.hpp>
#include <impl/Kokkos_TaskQueueCommon.hpp>
#include <impl/Kokkos_Memory_Fence.hpp>
#include <impl/Kokkos_Atomic_Increment.hpp>
#include <impl/Kokkos_OptionalRef.hpp>
#include <impl/Kokkos_LIFO.hpp>

#include <string>
#include <typeinfo>
#include <stdexcept>


//----------------------------------------------------------------------------
//----------------------------------------------------------------------------

namespace Kokkos {
namespace Impl {

//----------------------------------------------------------------------------
//----------------------------------------------------------------------------

template <
  class ExecSpace,
  class MemorySpace,
  class TaskQueueTraits,
  class MemoryPool
>
class SingleTaskQueue
  : public TaskQueueMemoryManager<ExecSpace, MemorySpace, MemoryPool>,
    public TaskQueueCommonMixin<SingleTaskQueue<ExecSpace, MemorySpace, TaskQueueTraits, MemoryPool>>
{
private:

  using base_t = TaskQueueMemoryManager<ExecSpace, MemorySpace, MemoryPool>;
  using common_mixin_t = TaskQueueCommonMixin<SingleTaskQueue>;

  struct EmptyTeamSchedulerInfo { };
  struct EmptyTaskSchedulingInfo { };

public:

  using task_queue_type = SingleTaskQueue; // mark as task_queue concept
  using task_queue_traits = TaskQueueTraits;
  using task_base_type = TaskNode<TaskQueueTraits>;
  using ready_queue_type = typename TaskQueueTraits::template ready_queue_type<task_base_type>;

  using team_scheduler_info_type = EmptyTeamSchedulerInfo;
  using task_scheduling_info_type = EmptyTaskSchedulingInfo;

  using runnable_task_base_type = RunnableTaskBase<TaskQueueTraits>;

  template <class Functor, class Scheduler>
    // requires TaskScheduler<Scheduler> && TaskFunctor<Functor>
  using runnable_task_type = RunnableTask<
    task_queue_traits, Scheduler, typename Functor::value_type, Functor
  >;

  using aggregate_task_type = AggregateTask<task_queue_traits, task_scheduling_info_type>;

  // Number of allowed priorities
  static constexpr int NumQueue = 3;

private:

  ready_queue_type m_ready_queues[NumQueue][2];

public:

  //----------------------------------------------------------------------------
  // <editor-fold desc="Constructors, destructors, and assignment"> {{{2

  SingleTaskQueue() = delete;
  SingleTaskQueue(SingleTaskQueue const&) = delete;
  SingleTaskQueue(SingleTaskQueue&&) = delete;
  SingleTaskQueue& operator=(SingleTaskQueue const&) = delete;
  SingleTaskQueue& operator=(SingleTaskQueue&&) = delete;

  explicit
  SingleTaskQueue(
    typename base_t::execution_space const&,
    typename base_t::memory_space const&,
    typename base_t::memory_pool const& arg_memory_pool
  )
    : base_t(arg_memory_pool)
  { }

  ~SingleTaskQueue() {
    for(int i_priority = 0; i_priority < NumQueue; ++i_priority) {
      KOKKOS_EXPECTS(m_ready_queues[i_priority][TaskTeam].empty());
      KOKKOS_EXPECTS(m_ready_queues[i_priority][TaskSingle].empty());
    }
  }

  // </editor-fold> end Constructors, destructors, and assignment }}}2
  //----------------------------------------------------------------------------

  KOKKOS_FUNCTION
  void
  schedule_runnable(
    runnable_task_base_type&& task,
    team_scheduler_info_type const& info
  ) {
    this->schedule_runnable_to_queue(
      std::move(task),
      m_ready_queues[int(task.get_priority())][int(task.get_task_type())],
      info
    );
    // Task may be enqueued and may be run at any point; don't touch it (hence
    // the use of move semantics)
  }

  KOKKOS_FUNCTION
  OptionalRef<task_base_type>
  pop_ready_task(
    team_scheduler_info_type const& info
  )
  {
    OptionalRef<task_base_type> return_value;
    // always loop in order of priority first, then prefer team tasks over single tasks
    for(int i_priority = 0; i_priority < NumQueue; ++i_priority) {

      // Check for a team task with this priority
      return_value = m_ready_queues[i_priority][TaskTeam].pop();
      if(return_value) return return_value;

      // Check for a single task with this priority
      return_value = m_ready_queues[i_priority][TaskSingle].pop();
      if(return_value) return return_value;

    }
    // if nothing was found, return a default-constructed (empty) OptionalRef
    return return_value;
  }

  KOKKOS_INLINE_FUNCTION
  constexpr team_scheduler_info_type
  initial_team_scheduler_info(int) const noexcept { return { }; }

};

} /* namespace Impl */
} /* namespace Kokkos */

//----------------------------------------------------------------------------
//----------------------------------------------------------------------------

#endif /* #if defined( KOKKOS_ENABLE_TASKDAG ) */
#endif /* #ifndef KOKKOS_IMPL_SINGLETASKQUEUE_HPP */

